Modern networks and network systems are typically constructed of multiple differing devices, elements, or links, referred to collectively herein as elements. These elements include communication devices that connect networks and other elements across a link. Links can be virtual links that connect through other communication devices or physical links that connect across physical wire, cables, wireless, or optical connections. Links can be of multiple protocols and physical connections and signaling methods. Telecommunication devices are specialized communication devices that connect networks and elements across links that are part of a telecommunications or phone system. Examples of such include, but are not limited to, digital subscriber line (DSL), ethernet links, modems, token ring, network hubs, network switches, wide area network (WAN) bridges, integrated services digital network (ISDN) devices, T1 termination units, etc. In particular, one recent such communications link and protocol is the high-speed digital subscriber line (HDSL), which has 2 wire and 4 wire variants.
Communication devices can have many physical configurations and implementations. Two popular physical configurations are the standalone enclosure and the line card chassis. Standalone enclosures, also called customer premise equipment (CPE) or remote (RMT) units, are typically used at end user sites or link terminal sites where only one device is required. Line card chassis, also called modular rack chassis, are popular in network hubs or telecommunication offices (also known as central offices or COs) where multiple communication links end and the density and central management capability of a line card chassis is an advantage. On a communication link such standalone or line card units are known as “terminal” units as they typically end or terminate the communication link.
Network communication distances have increased to the point where, in CPE communication device placements that are far from the CO communication device location, the signals from an originating communication device cannot easily reach the terminal or “far-end” communication device at the opposite end of the link. This has been additionally aggravated by the increasing device speeds and performance requirements of modern communication links and devices. The increased performance requirements and speed typically require an increased physical link quality and tend to further restrict the effective signaling distances of communication devices over the physical communication link. In these situations one or more signal repeaters or “doublers” may be used in the communication link to bridge the gap and enable the communication protocol to reach the receiving terminal communication device over lower quality physical links and/or at further distances from the originating device.
Many modern communication systems also typically have specifications that state how long a doubler can take to forward a received message to the next communication device or doubler in the communication link. This time period, for example, is 300 ms for a HDSL4 communication doubler. Other communication protocols that have similar forward timing requirements include, but are not limited to, HDSL2 and Single-pair High-speed Digital Subscriber Line (G.SHDSL).
With modern high performance communication links, in order to properly configure themselves, both communication devices at the opposite terminal ends of the link need to know how many doublers or other communication devices have been inserted in the link. This is also known as the “hop count” of the communication link. The communication devices therefore must either be informed of the number of doublers to expect on a communication link or go through a “discovery” phase to locate all intervening link doublers between it and the terminal communication device(s).
In discovery mode, an HDSL4 or HDSL2 communication device or doubler will send out a discovery query message over the communication link on an embedded operations channel (EOC) that is incorporated into the HDSL transfer protocol. The discovery query is received and repeated sequentially to all devices of the communication link. Each doubler and communication device in the communication link then sends back a response message to the querying device in turn that indicates their relative position in the communication link. This discovery process can happen either at communication device initialization or by insertion of the device into an operating communication link. The discovery process is concluded by a device performing discovery when a response is received from a terminal communication device. A problem can arise in discovery if a terminal communication device response is received before all of the intervening devices and doublers have responded. With the 300 ms message forwarding response time requirement of a communication link doubler such an occurrence is entirely possible, resulting in an incomplete hop count and an improperly configured communication device. It is also possible with the 300 ms messages forwarding response time, particularly on distorting or low quality physical links, to “corrupt” the message sequencing of the discovery response messages, such that the responses arrive out of order or even with the discovery response from a terminal communication device arriving before the remaining discovery messages of other doublers or communication devices in the link, prematurely closing the discovery process of the device performing discovery.
An additional problem can arise because of the message forwarding response time requirement of link doublers, in particular, the 300 ms message forwarding response time requirement in HDSL link doublers. With the forwarding response time of a communication link doubler it is possible for discovery responses from link devices to collide at a doubler if the device is responding to the discovery query as another response arrives from an upstream device. This can result in the corruption of one or more of the discovery response messages and/or sequencing of the discovery response messages and an incorrect count of intervening doublers and terminal communication devices being recorded by the device performing the discovery.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a method and apparatus of conveniently detecting link doublers that are utilized with communication devices and communication links.